The synthesis and gene expression of metallothionein, a metal binding protein which is developmentally regulated, will be studied in fetal and neonatal rat liver. This investigation will explore possible controls over metallothionein gene expression, including the ontogeny of hormone and metal ion inducibility and the developmental programming of metallothionein genes. Elucidation of the controls over transcription and posttranscriptional events in the biosynthesis of metallothionein will contribute to an understanding of how this protein functions during development in the metabolism of copper and zinc. The hormone inducibility of metallothionein makes this an ideal system for exploring the acquisition of hormonal responsiveness of tissues during development. This study will also explore the possibility that different genes and/or gene products are involved, or that metallothionein isoproteins are involved differentially, in the control of metallothionein synthesis during development. The mechanism of induction of metallothioneins by hormones or metal ions will be studied in rat liver in vivo and in primary hepatocyte culture, derived from fetal and neonatal tissue. Recombinant DNA techniques using rat liver cDNA and genomic sequences will allow accurate quantitation of mRNA levels in tissue, in examining transcriptional and posttranscriptional controls over mRNA formation, in searching for a multigene family of metallothionein-related-sequences from a rat genomic library, and in testing proposed mechanisms of metallothionein gene expression. This research will clarify the developmental role of metallothionein, help explain the mechanism of acquisition of the heavy metals zinc and copper by the fetus and neonate, and contribute to establishing why a strong evolutionary conservation is found for these proteins in eukaryotic organisms. Studying the ontogeny of metallothionein synthesis will add to our understanding of how the synthesis and degradation of this protein is influenced in diseases of metal metabolism, including Wilson's disease, Menkes kinky hair syndrome, acrodermatitis enteropathica and primary biliary cirrhosis.